It is known in the field of cellular radio telephones, for example, to use a memory module such as a data card which may be removably inserted into the telephone. Data, such as identity information, is read from the inserted card and used in the subsequent operation of the telephone. By way of example European Patent Application EP-A-0,369,110 discloses a mobile radio telephone having a handset into which a data card storing subscriber-related information is insertable for transferring information from the data card to the working memory of the telephone.
The data card may be, for example, a so-called "smart-card" which is similar in size to a conventional plastic credit card and which includes a memory implemented as an integrated circuit device, commonly referred to as a "chip", in which information is stored. For this reason such cards are also often known as "chip cards".
In addition to subscriber identity information, such as the subscriber telephone number, and personal identification number (PIN), the smart card may store for example, call charge information (i.e. a charge meter), a telephone number index, or false PIN entries. As memory capacity expands in smaller chip sizes, more applications can be implemented on one smart card. Accordingly, it is envisaged that in future multipurpose smart cards will cover an even wider range of applications than personal identification and datastorage services.
Indeed, in modern telecommunication systems, the applications for smart cards is expanding. One such application in this field is the so-called subscriber identity module (SIM) proposed for the pan-European digital cellular radio telephone system known as GSM (Group Speciale Mobile). For more information about the SIM proposed for GSM, reference is invited to the European Telecommunications Standards Institute (ETSI) Recommendation GSM 11.11 which describes the technical SIM specifications and Recommendation GSM 02.17 for the functional characteristics of the SIM.
There are currently two different mechanical standards proposed for the GSM SIM card and it is probable that a third will evolve. The functionality of the SIM is the same for all sizes, it is essentially that the physical dimensions are different. At present the two standards are (a) a credit card size SIM, and (b) a plug-in SIM about 20 mm.times.25 mm. The proposed third standard is likely to be a mid-sized SIM about half the size of a regular credit card. The rationale behind the different sizes is that the credit card size is perceived as a convenient size for the user from a practical standpoint. However, the credit card size is relatively large, and smaller card sizes are needed as miniaturization continues to drive down the overall size of the terminal (i.e. the radio telephone unit itself). The plug-in SIM is intended to be semi-permanently installed in the cellular telephone.
In future it is envisaged that compatibility problems are likely to arise when several different sizes of SIM are in wide use, because the SIM receiving device in a particular terminal will generally be designed to accept only one SIM type.